Serum IL-18/IL-13 Ratio Predicts Super Response to Secukinumab in Patients with Psoriasis

Identifying immunologic predictors of clinical response remains an unmet need in the era of biologic therapy for psoriasis. Super responders (SRs), defined as patients achieving complete skin clearance within weeks of treatment initiation, represent an emerging clinical endotype; however, their immunological underpinnings are poorly understood. We conducted a prospective observational study to characterize serum cytokine profiles associated with SR status in biologic-naïve patients with moderate-to-severe plaque psoriasis treated with secukinumab, an IL-17A inhibitor. Twenty-eight patients were enrolled and stratified at week 12 into SR (PASI = 0; n = 9) and non-super responder (NSR; PASI > 0; n = 19) groups. Serum concentrations of 19 cytokines were analyzed at baseline and after 12 weeks of treatment. SRs displayed a distinct immunological signature characterized by significantly higher IL-13 and lower IL-18 baseline levels compared to NSRs (p = 0.002 and p = 0.007, respectively), alongside reduced baseline monocyte counts. L1-regularized logistic regression confirmed IL-13 and IL-18 as strong independent predictors of SR status (AUC = 0.91). Moreover, the IL-18/IL-13 ratio emerged as a highly discriminative biomarker (p = 0.00001, AUC = 0.86). Notably, SRs exhibited a more pronounced decline in IL-18 and IL-23 during treatment. Our findings provide novel insights into the immunopathogenesis of super response and suggest that an immunological milieu favoring Th2 polarization may promote superior outcomes with IL-17A blockade. Incorporating IL-13, IL-18, and their ratio into clinical algorithms may facilitate precision-guided biologic therapy in psoriasis.